And finally, we looked at logic programming, and in the end, I told you that we're only

doing a third of the things we need to do when we want to build agents, namely, you

want to do deduction, which is basically maintaining your world model.

You have a couple of facts you know, you have a couple of facts you perceived, you want

to find out new facts.

Is the wampus near, or is the gold near?

But very often, you need more.

Very often, you need to make assumptions about the world, explain things that you're seeing,

because most of the facts you see, you need, you cannot see directly.

You have to kind of make explanation for them.

And that's a process called abduction, which is something you can do quite easily using

deduction.

Say you have a resolution proof, you have an initial clause set, you build, kind of

go forward, and at some point, you have a unit clause here.

Right?

Say something like of the form, street, no, rains, false.

Okay?

Now you want an empty clause, but you can't quite get it.

Well, then you cheat.

You say, ah, if I knew that it actually rained, I could make the empty clause.

So you can do deduction from this and this and da da da da da da, and then when you find

out, oh yes, I could end the deduction, I could prove those things by saying it rains,

then you do.

And that is an explanation.

If you think about it, if you can add something to complete a proof, then that's something

that you add to complete the proof is actually an explanation.

And very often, if you hear something, then you often need to combine what you hear with

your world knowledge and then kind of generate the causes why I have said something like

this.

If I meaningfully stare into your eyes and say, well, you know the exam is in two weeks,

that probably tells you more.

You probably want an explanation why I said that.

You probably want to say, oh yes, I want to pass the exam, and to pass the exam I have

to do my homework, and probably I should do them before the exam, and probably since they

take about 10 days to do, I should start doing this Saturday.

And then this start doing this Saturday, start doing homework Saturday is what I really wanted

to say, but I didn't.

But an explanation of why I could have said that, that's abduction.

And finally, induction is where you learn rule-like stuff, which is what we're going

to do next semester in various ways.